In the consumer slide projector market, the most successful design in recent years incorporates a circular slide receptacle or tray, for storage of the slides to be projected. In operation, the slide tray, which is mounted on top of the slide projector, is rotated about a fixed vertical axis so that the compartment containing the slide to be projected is in registry with the slide gate therebeneath. The slide moves through a slot in the bottom of the slide tray by gravity into the slide gate and is then projected. Following projection, the slide is moved by a mechanical lifter from the slide gate back into its compartment in the slide tray. The same process occurs for each slide to be projected.
Exemplary of this design currently on the market is a Kodak slide projector and its mating slide tray, sold, respectively, under the trademark Carousel. An example of a similar projector in the patent literature is U.S. Pat. No. 3,276,314 to Robinson. Such mechanically operated and controlled slide projectors have been extremely successful in the consumer slide projector market.
However, such conventional slide projectors have only one projection optics system, including a single projection lens. Thus, the previously projected slide must be moved from the slide gate back into its original compartment in the slide tray before the next slide can be moved into the gate and projected. This results in a delay between the projection of successive slides.
Lap-dissolve projector arrangements have been developed to eliminate this delay and provide a smooth transition between successive slides. In one solution, which is currently used extensively, several single optics slide projectors are operated together, controlled by an interface device. It is not uncommon for three or even more projectors to be used together for a sophisticated slide presentation.
Another solution is a single projector having multiple projection optics systems. However, significant difficulties have been encountered with such an arrangement, particularly with respect to the slide movement between the slide tray and the two optics systems. Initial attempts included two magazine-type slide trays, one for each optics system. Such an arrangement basically is two projectors contained in a single housing. The next development used a single magazine or drum slide tray in which slides were moved out of the slides of the slide tray. The slide tray was moved forwards and backwards in a particular sequence in order to maintain proper storage of the slides. Such a structure is shown in U.S. Pat. No. 3,462,215 to Floden. Although the optics systems for both of the above solutions are relatively simple, neither solution was usable with a circular slide tray.
Initial development of a multiple-optics slide projector which was capable of using a circular slide tray is shown in U.S. Pat. No. 3,501,233 to Winkler et al. However, the Winkler structure is quite complicated, includes a slide tray support structure in which the tray is alternately rocked about points on opposing sides of the tray, and more importantly, requires a careful initial positioning of the slides into two separate groups in the tray.
The next advance in the art is exemplified by U.S. Pat. No. 3,689,140 to Harvey, which teaches a circular slide tray and two projection optics systems, in which slides can be loaded in the tray in a normal sequence. However, the tray in operation is shifted laterally to access the two slide gates, as well as rotated. Such a structure is complex mechanically and expensive to implement. The next development in the art is exemplified by U.S. Pat. No. 4,165,161 to Kramer, which solved the problem of Harvey by using swinging slide gates, which moved in operation between a common load position and separate project positions. The Kramer structure, however, is also fairly complex and fairly sophisticated to both operate and maintain.
Thus, the lap-dissolve slide projectors known to the art at the time of applicant's invention were quite complex mechanically, particularly with respect to the tray drive system and/or the projection optics system, and in some cases required special loading of the slides in the slide tray.